The present invention relates to headlight for a vehicle, operating in accordance with projection principle and to an illumination device with at least one such headlight.
The German patent document DE 196 21 254 A1 discloses such a headlight. The headlight has a light source and a reflector by which light emitted by the light source is reflected. In a path of rays of a light bundle reflected by the reflector, a screening device is arranged and formed as a screen which screens a part of the light bundle reflected by the reflector and is not permeable for the light in visible wave length region. The screening device produces a bright-dark limit of the visible light exiting the headlight. In the light outlet direction after the screening device, a lens is arranged for passing the light reflected by the reflector and passed over the screening device. The screening device is required for producing the bright-dark limit, to prevent a blinding of the opposite traffic by the visible light. However, it limits a visibility range for the vehicle driver, so that he can not recognize objects located at a great distance since they are not eliminated.
Accordingly, it is an object of the present invention to provide a headlight for a vehicle operating in accordance with projection principle and an illumination device with at least one such headlight, which eliminate the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a headlight in which the screening device is at least partially permeable at least locally for light in infrared wavelength region and the light passing through the screening device in infrared wavelength region has a greater range than the light passing over the screening light in visible wavelength region.
When the headlight is designed in accordance with the present invention then, additionally to the illumination of the region in front of the vehicle with light in visible wavelength region, the region located at a great distance is illuminated with light in infrared wavelength region. This provides a possibility for an improvement in conditions of visibility for the vehicle driver, without blinding the opposite traffic. No additional components must be provided in the headlight when compared with the known solutions.
The illumination device designed in accordance with the present invention has a sensor device and an indicating device. It has the advantage that, due to the sensor device which detects the region illuminated in the infrared wavelength region, and the indicating device for the vehicle driver, the vehicle driver can also recognize objects located at a great distance.
In accordance with another embodiment of the present invention, the screening device is movable between a position in which it extends in the path of rays of the light bundle reflected by the reflector and another position in which it is located further in the path of rays. In this construction an additional high beam function with the light in visible wave length region is provided.
In accordance with another feature of present invention, the screening device at its side facing the reflector is at least partially reflective for light in visible wavelength region. In this construction the use of the light screened by the screening device is possible in the visible wavelength region.
In accordance with still another feature of the present invention the screening device is at least partially permeable locally for the light in infrared wavelength region and at least locally impermeable for the light in infrared wavelength region. In such a construction a desired determination of the region or regions which is/are illuminated with the light in infrared wavelengths regions is provided.
In still a further embodiment of the present invention, the light source operates with modulation, and the modulation frequency is preferably at least substantially 100 Hz. This eliminates an influence of light caused by the other light sources in the infrared wavelength region.
Finally, in the path of rays of the light passing over the screening device and in infrared wavelength region, a polarization device can be arranged with which the passing light is linearly polarized. This eliminates an influence of light caused by other light sources in infrared wavelength region as well.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.